My count of Duo-Art expression levels begins here:  Accomp = 16,
Theme = 16, now 32, plus sustaining pedal = 64 (the test roll, and
the coding of the rolls backs this one up), plus soft pedal = 128,
with both soft pedal, 256.

This does not take into account the possible use of A#2 on soft pedal,
or as on some instruments both A#2 and T#2 on soft pedal.  (Yeah, its
not in the '27 manual, but its there on some pianos.)  Then, too, there
are many later uprights that have no soft pedal pallet at all so, book
or no, it was never intended to be hooked up to A#2 -- but then many
earlier pianos in virgin condition never had A#2 hooked up (yeah, it's
not in the book either).  Then there's the double pallet tripped by the
A spill at 15 which opens the theme primaries.

Then there are the fan [expression] systems that have extra springs
that engage at about A#10 and T#10, that change the value added at
every level above 10.

Long smooth crescendos can be easily created, like an artist does,
without the use of an automatic crescendo.  (Do you know a pianist who
plays with an automatically timed crescendo?  That can be delightful,
too!)

Bruce Grimes